A series of iodinated and brominated perfluorochemicals was selected for study as possible x-ray contrast agents. The ring and straight chain iodinated fluorochemical compounds, while they are good oxygen solvents and excellent x-ray contrast agents are unstable under laboratory conditions, giving rise to free iodine in light. The brominated perfluorochemicals as a group were found to be stable and, in general, to make emulsions suitable for intravenous use. Their x-ray opacity is comparable to the iodinated substances and, in addition, at least two of the straight chain bromofluorocarbons studied leave the body rapidly. A long term study of bromoperfluorooctylbromide in a rhesus monkey is nearly complete. New methods for the detection and analysis of these substances in breath, from skin, and in blood and organs are being developed. Selected emulsions are being tested for angiography using non-human primates. In vivo and in vitro tests of phagocytosis in the handling and transport of emulsion particles is in progress. Studies of the effects on organ ultrastructure and in tumor location are underway. Our research is being extended to the study of a number of ring and straight chain bromofluorochemicals.